1. Field of the Invention
The present invention relates to a measurement circuit for measuring a device under test and a test apparatus including the measurement circuit. More particularly, the present invention relates to a measurement circuit for performing voltage-application current-measurement or current-application voltage-measurement.
2. Related Art
A direct-current test for a device under test has been known as a test item for the device under test such as a semiconductor circuit. Moreover, as a direct-current test, there is known a test for deciding the quality of a device under test based on a measurement result of voltage-application current-measurement for measuring a direct current supplied to the device under test when applying a predetermined direct voltage to the device under test and a test for deciding the quality of a device under test based on a measurement result of current-application voltage-measurement for measuring a direct voltage supplied to the device under test when supplying a predetermined direct current to the device under test.
Moreover, when performing this direct-current test, a measurement circuit including a circuit that restricts a direct current supplied to a device under test is known in order to prevent excess currents from being supplied to the device under test. FIG. 5 is a view exemplary showing a configuration of a conventional measurement circuit 400.
When applying a predetermined direct voltage to a device under test 300, the measurement circuit 400 is a circuit for measuring a direct current supplied to the device under test 300. A DA converter 402 generates a direct voltage to be applied to the device under test 300, and inputs it into a main amplifier 406. The main amplifier 406 generates an applied voltage according to this direct voltage, and applies it to the device under test 300. Moreover, this applied voltage is fed back to an input port of the main amplifier 406 in order to control the applied voltage output from the main amplifier 406 to a predetermined voltage.
A voltage detecting amplifier 412 detects a voltage of both ends of a current detecting resistor 408, and outputs a detecting voltage Vim obtained by amplifying this voltage. A DA converter 428 and a DA converter 416 output voltages according to a lower limit and an upper limit of a direct current supplied to the device under test 300.
For example, the DA converter 416 outputs an upper limit voltage according to the upper limit of the direct current. The upper limit voltage and the detecting voltage Vim are voltages having different polarity. Moreover, a voltage difference between the upper limit voltage and the detecting voltage Vim is divided by a resistor 418 and a resistor 420, and is input into an amplifier 414. For example, if an absolute value of the detecting voltage Vim becomes larger than an absolute value of the upper limit voltage, a positive voltage is input into a negative input terminal of the amplifier 414. As a result, the amplifier 414 outputs a negative voltage, and thus the state of a diode 424 becomes ON.
In this case, electric currents flow from the DA converter 402 to the diode 424. Since a voltage on the resistor 404 descends, an applied voltage applied to the device under test 300 descends, and a direct current flowing into the device under test 300 is restricted.
Now, since a related patent document is not recognized, the description is omitted.
However, in the conventional measurement circuit 400, a voltage output from the amplifier 414 is changed from the neighborhood of a power supply voltage of the amplifier 414 to the neighborhood of 0V. Since the fluctuation of voltage in a power point of the amplifier 414 is large, it was difficult that the conventional measurement circuit 400 performs current limiting at high speed.